II.3. INDOOR EXPOSURE TO HEAT

The National Human Activity Pattern Study conducted by the Environmental Protection Agency in the USA during 1990s shows that 87 % of their time Americans spend indoors, of which 69% at home and 18% at some other type of indoor venue (Klepeis et al., 2001). A 2011 poll in the UK indicated that on average the population spent outdoors only 17 minutes per day (Seddon, 2011). Although behavioral patterns differ across territories and in time, these studies give at least approximate understanding of the disproportionately large amounts of time spent by people indoors.

Climate change alters the conditions of living and affects the microclimate in buildings. Although IPCC mostly discusses construction and buildings in the context of GHG emissions reduction, it also mentions buildings in relation to thermal comfort (Levine et al., 2007). During a heat wave the exposure of people indoors to heat is conditioned by the thermal qualities of the building (thermal insulation, construction materials) and the ventilation and air conditioning systems installed in the building and of course by the outdoor environment (density of buildings, proximity of parks, etc. See “Outdoor exposure to heat waves and urban heat island effect”)

As pointed out by J.-L.Salagnac, CSTB, after some days of heat wave, regardless of thermal qualities of a building, the heat will penetrate in any kind of housing[1], if it’s not equipped with air conditioning system, the only difference is the time which the heat will take to arrive from outside.

The buildings which are not equipped with sun protection, operable windows or ventilation system, electricity and water supply; those with limited living space or not insulated expose their inhabitants to heat. On the other hand, the living conditions of households are mostly determined by their socio-economic characteristics, i.e. households with low income are likely to occupy the housing with the worst conditions, with the less living space, not all of them can afford to pay electricity bills or install an air conditioner. Thus, limited income produces inequality which further translates into vulnerability to hazard. Low income is not of course the only factor which makes the population sensitive, but one of the most powerful in producing inequality (Wisner et al., 2004), other population sensitivity factors are explored in “Population sensitivity”.

Returning to exposure factors, one of them is building’s thermal mass. In the buildings with high thermal mass heat is transferred slower through the building envelope. Construction materials accumulate heat during the day and release it when the outside temperature drops. The elements which enable high thermal mass are thermal insulation on the exterior part of the wall, thick and heavy walls made of concrete or stone) (Alessandrini et al., 2008). High thermal mass is beneficial during heat waves, especially during the first days, the inside is well protected from heat, but if the period of hot weather lasts a few weeks and it’s not possible to cool down the air inside, the thermal mass might bring discomfort (Alessandrini et al., 2008) , as the walls will cool down much slower than those with low thermal inertia.

Natural ventilation helps evacuate excess heat from a building if it’s ventilated at night, when outer temperature is lower than during the day. Yet during heat waves, the difference between day and night temperature is insignificant, so natural ventilation doesn’t give much relief. (Alessandrini et al., 2008) At the same time, non- operable windows significantly reduce comfort of residents.

Thermal characteristics of buildings are often in relation to the period of their construction: most popular construction materials, absence or type of thermal insulation, type of construction, urban form, all of these differ according to the period of construction. So the age of building can serve as an indicator of its thermal condition. Most buildings built before the end of the 19th century have thick walls and mostly have considerable thermal mass. In the beginning of the 20th century building atmospheres became more carefully controlled, more attention was paid to thermal insulation. After the WWII, the economies exhausted by war sought for cheaper and faster construction: prefabricated thinner structures appeared.

Right after the war and up to 1954 the major objective for the newly created Ministry of Reconstruction and Urbanism in France was to answer the urgency of housing demand. (Anderweg et al., 2007) Later, during the 1954- 1964 period the priority in housing policy was given mostly to social housing (HLM), large use of concrete and standardization was encouraged. It was in this period that “grands ensembles”, large housing estates first were built in Plaine Commune (Fery and Lahrech, 2012). During 1964 and up to 1974, the so called ZUP period, the building effort increased tremendously (around 3 mln buildings were built) (Anderweg et al., 2007)

In late 1970s after energy crisis, most building codes have set minimum requirements for insulation of building envelopes. France adopted its first thermal regulation in 1974, so homes built starting from 1975 are thermally insulated which proved to be very cost-effective in energy saving (Anderweg et al., 2007), as in a thermally insulated house heat takes longer to penetrate through the building envelope and thus is the inner temperature is kept unchanged for longer time[2].

If thermal characteristics of buildings differ according to building materials, type of insulation and, indirectly, to the period of construction, which types of buildings are the most easily penetrable for heat? Is there a way to generalize and point out types of buildings, vulnerable to heat penetration?

An attempt to make a typology of residential buildings was undertaken in IEE project TABULA. Building typologies for 13 European countries, including France, were developed. A web-based TABULA tool demonstrates buildings typology, which groups buildings according to their size, age and corresponding thermal characteristics. French buildings typology provided by TABULA project is presented in detail in Annex 3; it classifies the types of housing (house or apartment building) by years of construction and roofing materials and walls. Thermal characteristics of renovated houses are not taken into account. “Tabula Web Tool” developed in the framework of the same TABULA project, highlights the problems of insulation typical for different types of buildings and shortly describes possible scenarios of renovation and thermal insulation of buildings.

According to the classification, the buildings built during the period between WWII and 1974, are in general the most poorly insulated and are, therefore, the least energy efficient, the easiest for heat to penetrate. As previously mentioned, during this period many projects of social housing were launched to accommodate as quickly as possible with minimal cost many people in need of housing. The response to this challenge was the construction of “grands ensembles”, multistory buildings organized in large public housing developments, inspired by the principles of modern architecture, stipulated in the Athens Charter. The most famous (or notorious?) development is Cité des 4000 in La Courneuve, originally the neighborhood of 4000 apartments. (Fig. 23)

In most cases, large housing estates are subject to renovation (Fig. 24) or demolition, as for exemple, Renoir building in La Courneuve in 2001.

Not only thermal characteristics of building envelope are important to decrease or increase the vulnerability of the occupants, but also the location of the room in the building is important. As Roaf et al. pinpoint :

“The rooms on the roof are much more closely coupled to the fluctuating temperatures of the sky, while those sunk into the ground are coupled to a more stable earth temperature, with a far lower rate of change, responding to the changes in seasonal mean temperatures rather than the minute-to-minute temperature changes.” (Roaf et al., 2009)

There are many examples of the use of this vertical temperature distribution difference in vernacular architecture, for example Haveli in India (Fig.25 ) In some Asian houses the basements can be 9 m below ground level, providing cool stable temperature even when it sweltering hot outside. (Roaf et al., 2009)

Fig 25 Haveli, India. Time lag in heat penetration in the building (Roaf et al 2009)

No sun protection on windows, uninsulated roof, dormer windows are all factors which contribute to the exposure to heat of the residents of mansards and upper floors. (Alessandrini et al., 2008) Morbidity and mortality statistics of 2003 heat wave in France show that more than half of the victims lived on top floors. In many cases the emergency personnel reported that it was extremely hot in the rooms where the bodies were found, between 36 ˚C and 40˚ C (Poumadère et al., 2005). Chicagoans interviewed after the heat wave in 1995 also give evidence that the temperature was unbearable (48- 54 ° C) in apartments on the upper floors.

On the other hand, although the temperature is lower on the ground floor, some Chicagoans said they preferred not to sleep on the ground floor because they felt more vulnerable to break-in on the ground or first floor (Klinenberg 2002). Thus, safety issue in a neighborhood might influence inhabitants’ exposure to heat.

Horizontal temperature distribution in buildings depends on the orientation of the building, orientation and dimensions of windows, thermal characteristics of walls, sun protection equipment, etc. If southern and western walls are unprotected from the sunlight and if they are glazed heat easily penetrates inside the building. In general, the greater the surface of glazing facing the sun, the faster the temperature rises inside the building. (Fig. 26 and 27) Sun protection equipment is not always effective to protect from heat, especially the blinds or shades that are installed on the inner side of the window. Once solar radiation passes through the glass, it is absorbed and re-emitted at a different wave length, at which it can’t travel back outside. This phenomenon is the basis of greenhouse effect, and means that even with the blinds down, the building overheats (Roaf et al., 2009)

Fig.26 School building in Épinay-sur-Seine. West-facing façade with no sun protection is exposed to overheating

Source: photo by author

Fig.27 Private house in Épinay-sur-Seine. West-facing façade is well masked by trees from direct sunlight

Source: photo by author

The territory of Plaine Commune, with high population density and with a large proportion of housing and commercial premises is exposed to heat waves and thus to thermal discomfort for two major reasons: because of thermal quality of housing and commercial buildings and due to the outer environment of buildings (urban form, density, proximity of parks, etc.)

The housing stock in Plaine Commune consists of 172 936 dwellings (Filocom 2011), 95% are primary residences. 68% of the housing stock of Plaine Commune was built before the first thermal regulation was introduced and consequently doesn’t have the best thermal quality and bioclimatic condition.

Apart from the date of construction, the overall quality of housing assumes a high vulnerability to climate extremes: 8% of the private park is considered to be “uncomfortable” and 20% as “substandard” (CDT, 2013). 5.4% of housing in Plaine Commune is vacant (INSEE 2010), it’s mostly private housing. Private housing has comparatively older, smaller and less well equipped dwellings (INSEE, 2010) According to evidence by M. Bardou, Agenda 21 project manager in delegation to urban ecology, fraudsters operate on private housing market, the so-called “marchands de sommeil”, who rent apartments, or rather cots to the most vulnerable population, to those who can’t afford better. These kind of apartments are neglected, not repaired, and often overpopulated.

Individual houses (13% of residential park, highest concentration in Pierrefitte-sur-Seine- 34%, Stains – 28%, Villetaneuse – 23%) are mostly occupied by owners (79,5%), generally private individual housing is in worse condition and is more energy inefficient than the housing, provided by social housing organizations.(INSEE 2010)[3] The occupants of individual houses are exposed to the uncomfortable thermal conditions due to the fact that in general these are older buildings with considerable thermal mass and after several days of heat exposure requiring more energy to cool down with the use of air conditioning. (Table 8)

Social housing, which is mostly represented by multistory apartment buildings (87%, INSEE 2009), is partly exposed to uncomfortable thermal conditions and heat related illnesses during heat waves in another way: the apartments on upper floors and/ or facing South, South-West and West gain the most heat.

In addition to high exposure to heat-related illness and uncomfortable conditions, sensitivity of the population is rather high. Several economic indicators point to the high sensitivity of population (renters and homeowners):

The observed overcrowding of housing: 44% of tenants and 19% of homeowners live in overcrowded conditions;

The standard of living of the people has an effect on their sensitivity to heat, to the extent that it affects the ability to invest for the thermal rehabilitation of housing, air conditioning system installation and the ability to pay energy bills for cooling.

Table 8. Residential park of Plaine Commune Source: INSEE 2009

Territory

Number of dwellings

Number of individual houses

Number of apartment buildings

Percentage of individual houses

Saint-Ouen

22826

1194

20508

5%

L’Île-Saint-Denis

2968

157

2732

5%

Aubervilliers

30502

2322

27254

8%

Saint-Denis

43538

3737

37841

9%

La Courneuve

13884

1998

11575

14%

Épinay-sur-Seine

20536

3324

16983

16%

Villetaneuse

4362

987

3298

23%

Stains

12558

3499

8743

28%

Pierrefitte-sur-Seine

10206

3481

6590

34%

Plaine Commune

161381

20699

135524

13%

In this context, the increase in the frequency and intensity of heat waves could lead to summer fuel poverty. The share of income spent on energy budget by households of Plaine Commune, called rate of energy effort is 5.4%, compared to 3.4% in Ile-de-France (Intelligent Energy Europe, 2012).

The territory of Plaine Commune is experiencing a massive development of tertiary activities over the past ten years, marked by the installation of large businesses like Orange. This dynamic, which is explained by proximity of the territory to Paris and the availability of land (including the redeveloped areas, former industrial wasteland) let Plaine Commune to become “one of the major commercial centers of the region” (CDT, 2013) (Table 9)

If it is difficult to estimate the thermal and bioclimatic quality of offices built in recent years, taking into account that the principles of bioclimatic architecture and passive solar design remain relatively marginal in construction projects. Most of the projects on the territory generally provide the buildings with ventilation systems and air conditioning, in this way making them inefficient in terms of energy and even more vulnerable in case of disruption of electricity supply.

Table 9. Share of service companies on the total enterprises in the territory Source CLAP data base, INSEE, 2010

Percentage of dwellings constructed before the first thermal regulation (1975) in the residential park (source : ROSE, 2009)

68%

Percentage of population eligible for social housing (Contrat de Développement Territorial, 2013)

80%

Population under poverty line (Contrat de Développement Territorial, 2013)

1/3

Percentage of service companies in total number of active companies (base de données CLAP, INSEE, 2010)

73%

The importance of urban renewal programs (24 ANRU projects comprising 58,000 units, 3,750 new housing demolitions and 6350) and the rehabilitation of old housing (two PRNQAD – National programs redevelopment of old neighborhoods in Aubervilliers and Saint Denis) is another characteristic feature of territory.

The construction and renovation of buildings (residential and commercial) are very important issues for Plaine Commune, both socio-economically due to high demand for housing and office space, fight against substandard housing, and in terms of the thermal quality (fight against fuel poverty, improving thermal insulation of the housing. Consideration of thermal comfort in summer within this framework will become an important issue due to rising temperatures and the frequency of heat waves. Potential directions in the context of adaptation planning in this impact would be to consider summer comfort in the construction / renovation of housing and business space.

[1] The present article will concern mostly housing, as people spend most of their time inside homes. On the other hand, commercial buildings and offices are mostly equipped with mechanic ventilation and air conditioning systems, which provide better conditions during a heat wave than homes.

[3]Bailleurs sociaux (fr) social housing management organizations, which can be public (OPH – office public de l’habitat) or private (ESH – entreprise social pour l’habitat). Plaine Commune Habitat is the public organization operating on the territory Plaine Commune is in charge of construction and management of most of the social housing on the territory of Plaine Commune